package net.monitor.common;

public class Base64Util {

    static final char[] intToBase64 = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.', '_'};

    static final byte[] base64ToInt = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 63, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51};

    public static String byteArrayToBase64(byte[] a) {
        int aLen = a.length;
        int numFullGroups = aLen / 3;
        int numBytesInPartialGroup = aLen - 3 * numFullGroups;
        int resultLen = 4 * ((aLen + 2) / 3);
        StringBuffer result = new StringBuffer(resultLen);

        int inCursor = 0;
        for (int i = 0; i < numFullGroups; i++) {
            int byte0 = a[(inCursor++)] & 0xFF;
            int byte1 = a[(inCursor++)] & 0xFF;
            int byte2 = a[(inCursor++)] & 0xFF;
            result.append(intToBase64[(byte0 >> 2)]);
            result.append(intToBase64[(byte0 << 4 & 0x3F | byte1 >> 4)]);
            result.append(intToBase64[(byte1 << 2 & 0x3F | byte2 >> 6)]);
            result.append(intToBase64[(byte2 & 0x3F)]);
        }

        if (numBytesInPartialGroup != 0) {
            int byte0 = a[(inCursor++)] & 0xFF;
            result.append(intToBase64[(byte0 >> 2)]);

            if (numBytesInPartialGroup == 1) {
                result.append(intToBase64[(byte0 << 4 & 0x3F)]);
                result.append("==");
            } else {
                int byte1 = a[(inCursor++)] & 0xFF;
                result.append(intToBase64[(byte0 << 4 & 0x3F | byte1 >> 4)]);
                result.append(intToBase64[(byte1 << 2 & 0x3F)]);
                result.append('=');
            }
        }

        return result.toString();
    }

    public static byte[] base64ToByteArray(String s) throws Exception {
        int sLen = s.length();
        int numGroups = sLen / 4;
        if (4 * numGroups != sLen) {
            throw new IllegalArgumentException("字串长度必须是4的倍数");
        }
        int missingBytesInLastGroup = 0;
        int numFullGroups = numGroups;
        if (sLen != 0) {
            if (s.charAt(sLen - 1) == '=') {
                missingBytesInLastGroup++;

                numFullGroups--;
            }

            if (s.charAt(sLen - 2) == '=') {
                missingBytesInLastGroup++;
            }
        }

        byte[] result = new byte[3 * numGroups - missingBytesInLastGroup];
        try {
            int inCursor = 0;
            int outCursor = 0;
            for (int i = 0; i < numFullGroups; i++) {
                int ch0 = base64toInt(s.charAt(inCursor++), base64ToInt);
                int ch1 = base64toInt(s.charAt(inCursor++), base64ToInt);
                int ch2 = base64toInt(s.charAt(inCursor++), base64ToInt);
                int ch3 = base64toInt(s.charAt(inCursor++), base64ToInt);
                result[(outCursor++)] = ((byte) (ch0 << 2 | ch1 >> 4));
                result[(outCursor++)] = ((byte) (ch1 << 4 | ch2 >> 2));
                result[(outCursor++)] = ((byte) (ch2 << 6 | ch3));
            }
            if (missingBytesInLastGroup != 0) {
                int ch0 = base64toInt(s.charAt(inCursor++), base64ToInt);
                int ch1 = base64toInt(s.charAt(inCursor++), base64ToInt);

                result[(outCursor++)] = ((byte) (ch0 << 2 | ch1 >> 4));

                if (missingBytesInLastGroup == 1) {
                    int ch2 = base64toInt(s.charAt(inCursor++), base64ToInt);
                    result[(outCursor++)] = ((byte) (ch1 << 4 | ch2 >> 2));
                }
            }
        } catch (Exception e) {
            throw e;
        }
        return result;
    }

    private static int base64toInt(char c, byte[] alphaToInt) throws Exception {
        int result = alphaToInt[c];
        if (result < 0)
            throw new Exception("非法索引值");
        return result;
    }
}